promisify-child-process


seriously like the best async child process library

(I'm joking, you may want to use execa which has a lot more features. The minor advantages of this package are:)

- it's a dual CJS/ESM package
- it conforms to the child_process API
- and it provides wrappers for all the async child_process functions

Based upon child-process-async,
but more thorough, because that package doesn't seem very actively maintained.

promisify-child-process provides a drop-in replacement for the
original child_process functions, not just duplicate methods that
return a Promise. So when you call exec(...) we still return a
ChildProcess instance, just with .then(), .catch(), and .finally() added to
make it promise-friendly.

Install and Set-up

``sh
npm install --save promisify-child-process
`

If you are using a old version of Node without built-in Promises or
Object.create, you will need to use polyfills (e.g. @babel/polyfill).

`js
// OLD:
const { exec, spawn, fork, execFile } = require('child_process')
// NEW:
const { exec, spawn, fork, execFile } = require('promisify-child-process')
`

Upgrading to v3

You must now pass maxBuffer or encoding to spawn/fork if you want to
capture stdout or stderr.

Resolution/Rejection

The child process promise will only resolve if the process exits with a code of 0.
If it exits with any other code, is killed by a signal, or emits an 'error' event,
the promise will reject.

Capturing output

exec and execFile capture stdout and stderr by default. But spawn and
fork don't capture stdout and stderr unless you pass an encoding or
maxBuffer option:

`js
const { spawn } = require('promisify-child-process');

async function() {
// captures output
const { stdout, stderr } = await spawn('ls', [ '-al' ], {encoding: 'utf8'});
const { stdout, stderr } = await spawn('ls', [ '-al' ], {maxBuffer: 200 * 1024});

// BUG, DOESN'T CAPTURE OUTPUT:
const { stdout, stderr } = await spawn('ls', [ '-al' ]);
}
`

Additional properties on rejection errors

If the child process promise rejects, the error may have the following additional
properties:

- code - the process' exit code (if it exited)
- signal - the signal the process was killed with (if it was killed)
- stdout - the captured stdout (if output capturing was enabled)
- stderr - the captured stderr (if output capturing was enabled)

Wrapper

If for any reason you need to wrap a ChildProcess you didn't create,
you can use the exported promisifyChildProcess function:

`js
const { promisifyChildProcess } = require('promisify-child-process');

async function() {
const { stdout, stderr } = await promisifyChildProcess(
some3rdPartyFunctionThatReturnsChildProcess(),
{ encoding: 'utf8' }
)
}
`

Examples

$3

`js
async function() {
const { stdout, stderr } = await exec('ls -al');
// OR:
const child = exec('ls -al', {});
// do whatever you want with child here - it's a ChildProcess instance just
// with promise-friendly .then() & .catch() functions added to it!
child.stdin.write(...);
child.stdout.pipe(...);
child.stderr.on('data', (data) => ...);
const { stdout, stderr } = await child;
}
`

$3

`js
async function() {
const { stdout, stderr, code } = await spawn('ls', [ '-al' ], {encoding: 'utf8'});
// OR:
const child = spawn('ls', [ '-al' ], {});
// do whatever you want with child here - it's a ChildProcess instance just
// with promise-friendly .then() & .catch() functions added to it!
child.stdin.write(...);
child.stdout.pipe(...);
child.stderr.on('data', (data) => ...);
const { stdout, stderr, code } = await child;
}
``